US3187237A - Permanent magnet assembly - Google Patents

Permanent magnet assembly Download PDF

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Publication number
US3187237A
US3187237A US191130A US19113062A US3187237A US 3187237 A US3187237 A US 3187237A US 191130 A US191130 A US 191130A US 19113062 A US19113062 A US 19113062A US 3187237 A US3187237 A US 3187237A
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Prior art keywords
magnets
magnet assembly
yoke
gap
extending
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US191130A
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Craig Robert Derek
Williams John Lewis
Willdig Edward
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Associated Electrical Industries Ltd
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Associated Electrical Industries Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets

Definitions

  • the present invention relates to magnet assemblies and in particular to magnet assemblies which produce a steady, high intensity homogeneous magnetic field which can be used, for example, in magnetic resonance spectrometers.
  • the object of the present invention is to provide a magnet assembly which produces a magnetic field tending to satisfy the above requirements.
  • a magnet assembly comprises two permant magnets extending axially towards each other and separated by a gap in which is produced a high intensity magnetic field together with a cylindrical yoke of a good thermally conducting material connecting said magnets and extending coaxially around said magnets.
  • the yoke may be formed with an aperture through which an object may be passed into the field produced between the two magnets,
  • the yoke comprises a movable member which may be moved in order to change the reluctance of the magnet circuit.
  • the adjacent surfaces of the magnets forming the gap may be flat and parallel or suitably shaped to ensure that the magnetic field is homogeneous over its central region by reducing the radial variation of the field strength due to edge effects.
  • the magnet assembly comprises two powerful permanent magnets 1, 2 having pole pieces 3, 4 respectively. These two magnets each of which may comprise a number of discs, extend axially towards each other so that the pole pieces are separated by a small gap which may be filled by a non-magnetic spacer.
  • the magnets are mounted on two end plates 5, 6 or" high permeability material by clamps 7, 8 of nonmagnetic material and the two end plates are connected by a cylindrical member 9 of material of high permeability and good thermal conductivity.
  • the yoke of the magnet assembly is formed by the cylindrical member 9 in combination with the end plates 5, 6 and hence completely surrounds the magnets 1, 2 and the high intensity field produced in the gap between them, and extends coaxially with the two magnets.
  • the yoke screens the magnets from any external stray fields and ensures the good distribution of heat throughout the assembly.
  • the yoke may be lagged internally and externally and mounted on thermally insulating supports 1i).
  • the space 11 within the yoke may be filled with a thermally insulating material such as polystyrene foam.
  • the yoke is formed with an aperture 12 through which objects may be passed into the gap between the pole pieces 3, 4. This aperture is utilized when the magnet assembly is used in a magnetic resonance spectrometer as described above.
  • the end plate 5 includes a slug 13 of high permeability material which may be moved relative to the end plate by suitable means, such as a screw jack mechanism 16.
  • suitable means such as a screw jack mechanism 16.
  • the movement of the slug 13 alters the reluctance of the magnetic circuit of the yoke and enables the strength of the field between the pole pieces to be varied.
  • the surfaces of the pole pieces 3, 4 defining the gap are essentially parallel, but may be suitably shaped to counteract edge effects which produce a radial variation of field strength over the central region when a very intense field is produced between the magnets 1, 2.
  • each magnet is tapered towards its associated pole piece, as illustrated.
  • the yoke substantially screens the space 11 magnetically and the good thermal conductivity of the material of the yoke ensures that any increase in temperature takes place evenly throughout the whole assembly, and hence there is substantially no distortion of the assembly which would affect the homogeneity of the field.
  • the crystal for the oscillator is located in a container 14 within the yoke of the magnet assembly and leads 15 connect the crystal with the associated equipment. The temperature stability of both the crystal and the magnet assembly will then be the same and any additional means used to stabilize the temperature of the magnet assembly will simultaneously stabilize the temperature ofthe crystal in the container 14.
  • the magnet assembly described may be enclosed in a container 17.
  • This container is made from material of high magnetic permeability and has an end plate 1d providing access to the slug 13 and an aperture 19 providing access to the aperture 12 and the gap between the magnet poles.
  • the magnet assembly is supported from the container on the thermally insulating supports 1).
  • a magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic eld, and means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a good thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets.
  • a magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, means providing a screen against external magnetic fields and protection against ambient temperature Variations comprising a cylindrical yoke of a good thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets, and a container of a material of a high magnetic permeability surrounding said yokey and thermally insulated therefrom.
  • a magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, said adjacent ends being suitably shaped so as to counteract edge eliects which tend to produce a radial variation of the field strength
  • means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a goodthermally conducting high permeability material connecting said magnets and extending co-axiallyl around said magnets, and thermal insulating means surrounding said magnets and enclosedby said yoke.
  • a magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a good i thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets, a movable portion to said yoke, and means for moving said movable portion so as to vary the reluctance of the magnetic circuit of the yoke.
  • a magnet assembly comprising two magnets extending axially toward each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, a yoke assembly comprising opposite end members on which said magnets are mounted and a cylindrical member extending between said, end members in surrounding relation to said magnets,r said yoke members all being of high magnetic permeability and coacting to substantially completelyv shieldingly enclose said magnets, and said cylindrical members being of good thermal conductivity for even distribution of temperature in the assembly.

Description

June 1, 1965 R. D. CRAIG ETAL 3,187,237
PERMANENT MAGNET ASSEMBLY Filed April4 50, 1962 ROBERT DEREK CRM@ :mm Laws wlLLm/us Emo/*Rn WILLDIG Bs; Immi- BauR/Mam,
United States Patent C 3,187,237 PERMANENT MAGNET ASSEMBLY Robert Derek Craig, Bowdon, John Lewis Williams, Wilmslow, and Edward Willdig, Stretford, England, assignors to Associated Electrical Industries Limited, London, England, a British company Filed Apr.. 30, 1962, Ser. No. 191,130 Claims priority, application Great Britain, May 2, 1961, 15,883/61 Claims. (Cl. 317-158) The present invention relates to magnet assemblies and in particular to magnet assemblies which produce a steady, high intensity homogeneous magnetic field which can be used, for example, in magnetic resonance spectrometers.
In such spectrometers it is necessary to have a magnet assembly which produces a high intensity magnetic field. The specimen under analysis is inserted into this field and associated apparatus which is sensitive to the gyromagnetic resonance of either the nuclei or the electrons of the specimen is used to analyze the specimen in a well known manner. The field produced by the magnet assembly must be homogeneous and steady, at least over the central portion of its extent, and must be substantially unaffected by ambient temperature changes or by stray magnetic fields.
The object of the present invention is to provide a magnet assembly which produces a magnetic field tending to satisfy the above requirements.
According to the present invention a magnet assembly comprises two permant magnets extending axially towards each other and separated by a gap in which is produced a high intensity magnetic field together with a cylindrical yoke of a good thermally conducting material connecting said magnets and extending coaxially around said magnets.
The yoke may be formed with an aperture through which an object may be passed into the field produced between the two magnets,
According to a preferred embodiment of the invention the yoke comprises a movable member which may be moved in order to change the reluctance of the magnet circuit.
The adjacent surfaces of the magnets forming the gap may be flat and parallel or suitably shaped to ensure that the magnetic field is homogeneous over its central region by reducing the radial variation of the field strength due to edge effects.
In order that the invention may be more readily understood reference will now be made to the accompanying drawing in which the single figure is a side view, sectioned on an axial plane, of a magnet assembly embodying the invention.
With reference to this figure the magnet assembly comprises two powerful permanent magnets 1, 2 having pole pieces 3, 4 respectively. These two magnets each of which may comprise a number of discs, extend axially towards each other so that the pole pieces are separated by a small gap which may be filled by a non-magnetic spacer. The magnets are mounted on two end plates 5, 6 or" high permeability material by clamps 7, 8 of nonmagnetic material and the two end plates are connected by a cylindrical member 9 of material of high permeability and good thermal conductivity.
The yoke of the magnet assembly is formed by the cylindrical member 9 in combination with the end plates 5, 6 and hence completely surrounds the magnets 1, 2 and the high intensity field produced in the gap between them, and extends coaxially with the two magnets. The yoke screens the magnets from any external stray fields and ensures the good distribution of heat throughout the assembly. The yoke may be lagged internally and externally and mounted on thermally insulating supports 1i). The space 11 within the yoke may be filled with a thermally insulating material such as polystyrene foam.
The yoke is formed with an aperture 12 through which objects may be passed into the gap between the pole pieces 3, 4. This aperture is utilized when the magnet assembly is used in a magnetic resonance spectrometer as described above.
The end plate 5 includes a slug 13 of high permeability material which may be moved relative to the end plate by suitable means, such as a screw jack mechanism 16. The movement of the slug 13 alters the reluctance of the magnetic circuit of the yoke and enables the strength of the field between the pole pieces to be varied. The surfaces of the pole pieces 3, 4 defining the gap are essentially parallel, but may be suitably shaped to counteract edge effects which produce a radial variation of field strength over the central region when a very intense field is produced between the magnets 1, 2. In order to increase the maximum eld strength obtainable each magnet is tapered towards its associated pole piece, as illustrated.
It will be seen that with such a magnet assembly, the chances of the magnetic field provided by the magnets 1, 2 between the pole pieces 3, 4 being affected by stray external fields or changes in temperature are very considerably reduced. The yoke substantially screens the space 11 magnetically and the good thermal conductivity of the material of the yoke ensures that any increase in temperature takes place evenly throughout the whole assembly, and hence there is substantially no distortion of the assembly which would affect the homogeneity of the field.
When the magnet assembly is used in a magnetic resonance spectrometer a crystal oscillator is sometimes used in the associated equipment. The frequency of such an oscillator will depend on the temperature of the crystal, and the field strength of the magnet assembly will also depend on the temperature of the assembly. It is essential that the frequency and the field strength should be constant relative to one another, whereas both can vary with temperature. Therefore, in accordance with a preferred arrangement, the crystal for the oscillator is located in a container 14 within the yoke of the magnet assembly and leads 15 connect the crystal with the associated equipment. The temperature stability of both the crystal and the magnet assembly will then be the same and any additional means used to stabilize the temperature of the magnet assembly will simultaneously stabilize the temperature ofthe crystal in the container 14.
In order to screen the magnets from stray magnetic fields even more eticiently the magnet assembly described may be enclosed in a container 17. This container is made from material of high magnetic permeability and has an end plate 1d providing access to the slug 13 and an aperture 19 providing access to the aperture 12 and the gap between the magnet poles. The magnet assembly is supported from the container on the thermally insulating supports 1).
What we claim is:
1. A magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic eld, and means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a good thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets.
2. A magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, means providing a screen against external magnetic fields and protection against ambient temperature Variations comprising a cylindrical yoke of a good thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets, and a container of a material of a high magnetic permeability surrounding said yokey and thermally insulated therefrom.
3. A magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, said adjacent ends being suitably shaped so as to counteract edge eliects which tend to produce a radial variation of the field strength Within the gap, means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a goodthermally conducting high permeability material connecting said magnets and extending co-axiallyl around said magnets, and thermal insulating means surrounding said magnets and enclosedby said yoke.
4. A magnet assembly comprising two magnets extending axially towards each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, means providing a screen against external magnetic fields and protection against ambient temperature variations comprising a cylindrical yoke of a good i thermally conducting high permeability material connecting said magnets and extending co-axially around said magnets, a movable portion to said yoke, and means for moving said movable portion so as to vary the reluctance of the magnetic circuit of the yoke.
5. A magnet assembly comprising two magnets extending axially toward each other with their adjacent ends defining a gap in which is produced a high intensity magnetic field, a yoke assembly comprising opposite end members on which said magnets are mounted and a cylindrical member extending between said, end members in surrounding relation to said magnets,r said yoke members all being of high magnetic permeability and coacting to substantially completelyv shieldingly enclose said magnets, and said cylindrical members being of good thermal conductivity for even distribution of temperature in the assembly.
References Citedv by the Examiner UNITED STATES PATENTS 3,018,422 1/62 Seaton 317-158 3,030,556 4/62 Watson 317-158 3,056,070 9/62 Nelson 317-158 JOHN F. BURNS, Primary Examiner.
E. JAMES SAX, Examiner.

Claims (1)

1. A MAGNET ASSEMBLY COMPRISING TWO MAGNETS EXTENDING AXIALLY TOWARDS EACH OTHER WITH THEIR ADJACENT ENDS DEFINING A GAP IN WHICH IS PRODUCED A HIGH INTENSITY MAGNETIC FIELD, AND MEANS PROVIDING A SCREEN AGAINST EXTERNAL MAGNETIC FIELDS AND PROTECTION AGAINST AMBIENT TEMPERATURE VARIATIONS COMPRISING A CYLINDRICAL YOKE OF A GODD THERMALLY CONDUCTING HIGH PERMEABILITY MATERIAL CONNECTING SAID MAGNETS AND EXTENDING CO-AXIALLY AROUND SAID MAGNETS.
US191130A 1961-05-02 1962-04-30 Permanent magnet assembly Expired - Lifetime US3187237A (en)

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Application Number Priority Date Filing Date Title
GB15883/61A GB949071A (en) 1961-05-02 1961-05-02 Improvements relating to magnet assemblies

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3250961A (en) * 1963-04-16 1966-05-10 Perkin Elmer Ltd Magnet assembly having thermal means to adjust the field strength thereof
US3423670A (en) * 1964-08-07 1969-01-21 Perkin Elmer Ltd Magnetic shield arrangement for a high flux homogeneous field-producing magnet
US3437963A (en) * 1967-06-12 1969-04-08 Varian Associates Permanent magnet having an enclosing yoke structure with pole aligning means
US3460083A (en) * 1967-06-12 1969-08-05 Varian Associates Permanent magnet employing an adjustable shunt internally of the permanent magnet structure
US3489894A (en) * 1966-07-21 1970-01-13 High Voltage Engineering Corp High power chamber
US4484161A (en) * 1982-05-24 1984-11-20 Varian Associates, Inc. Silicone rubber for relieving stress in magnetic material
US4585994A (en) * 1983-07-15 1986-04-29 Henry Ford Hospital Nuclear magnetic resonance imaging system
US4609109A (en) * 1982-07-06 1986-09-02 Cryogenic Consultants Limited Superconducting magnetic separators
US5122277A (en) * 1990-04-04 1992-06-16 Jones Clifford I Magnetic conditioner for fluid flow line
US5218333A (en) * 1989-10-02 1993-06-08 Sumitomo Special Metal Co., Ltd. Magnetic field generating device for use with ESR device
US5389879A (en) * 1992-12-18 1995-02-14 Pulyer; Yuly M. MRI device having high field strength cylindrical magnet with two axially spaced electromagnets

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474222A (en) * 1967-06-12 1969-10-21 Varian Associates Oven regulated permanent magnet having thermal lagging between the oven and the magnet
GB2132918B (en) * 1982-12-17 1986-11-19 De Beers Ind Diamond Magnetic separator roll

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3018422A (en) * 1959-11-16 1962-01-23 Norman T Seaton Variable-field permanent magnet
US3030556A (en) * 1957-10-18 1962-04-17 Fairey Aviat Ltd Nuclear magnetic resonance detectors
US3056070A (en) * 1957-09-27 1962-09-25 Varian Associates Magnet adjusting method and apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3056070A (en) * 1957-09-27 1962-09-25 Varian Associates Magnet adjusting method and apparatus
US3030556A (en) * 1957-10-18 1962-04-17 Fairey Aviat Ltd Nuclear magnetic resonance detectors
US3018422A (en) * 1959-11-16 1962-01-23 Norman T Seaton Variable-field permanent magnet

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3250961A (en) * 1963-04-16 1966-05-10 Perkin Elmer Ltd Magnet assembly having thermal means to adjust the field strength thereof
US3423670A (en) * 1964-08-07 1969-01-21 Perkin Elmer Ltd Magnetic shield arrangement for a high flux homogeneous field-producing magnet
US3489894A (en) * 1966-07-21 1970-01-13 High Voltage Engineering Corp High power chamber
US3437963A (en) * 1967-06-12 1969-04-08 Varian Associates Permanent magnet having an enclosing yoke structure with pole aligning means
US3460083A (en) * 1967-06-12 1969-08-05 Varian Associates Permanent magnet employing an adjustable shunt internally of the permanent magnet structure
US4484161A (en) * 1982-05-24 1984-11-20 Varian Associates, Inc. Silicone rubber for relieving stress in magnetic material
US4609109A (en) * 1982-07-06 1986-09-02 Cryogenic Consultants Limited Superconducting magnetic separators
US4585994A (en) * 1983-07-15 1986-04-29 Henry Ford Hospital Nuclear magnetic resonance imaging system
US5218333A (en) * 1989-10-02 1993-06-08 Sumitomo Special Metal Co., Ltd. Magnetic field generating device for use with ESR device
US5122277A (en) * 1990-04-04 1992-06-16 Jones Clifford I Magnetic conditioner for fluid flow line
US5389879A (en) * 1992-12-18 1995-02-14 Pulyer; Yuly M. MRI device having high field strength cylindrical magnet with two axially spaced electromagnets

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GB949071A (en) 1964-02-12

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